1. Field of the Invention
The present invention generally relates to a multi-camera imaging system, and a compensation method for image reconstruction; more particularly, to a system and method for generating image reconstruction parameters for a multi-camera imaging system when a displacement of any change of distance between the multi-lens module and the multi-sensor module is found.
2. Description of Related Art
Reference is made to FIG. 1 which schematically shows a conventional matrix-array camera. The matrix-array camera includes multiple cameras. Every camera includes a set of lenses and a corresponding image sensor. Thus the matrix-array camera includes a multi-lens module and a multi-sensor module. For example, the shown lens array 101 is an essential component of the matrix-array camera. Multiple arrayed image sensors (not shown in this diagram) are correspondingly disposed below the lens array 101. The matrix-array camera also requires an outer carrier mechanism 10.
A specific space exists between the adjacent lenses of the lens array (101) within the multi-lens module shown in the diagram. The space between the lenses causes a parallax when the camera captures images from the multiple lenses by shooting the same scene where an object is located. Therefore, the matrix-array camera incorporates a software or hardware utility to reconstruct the plurality of images for gaining a merged picture. The image reconstruction process requires reconstruction parameters to calibrate the plurality of imaging positions and imaging ranges, in order to obtain a correct merged picture of excellent quality. In addition, the matrix-array camera may have smaller volume.
Regarding the focusing system of the camera, a focus for gaining a clear image makes a space between the lens and an image sensor. Referring to an optical imaging equation (1/u+1/v=1/f), the variable u indicates an object distance (u) between the lens and the scene; the variable v indicates an image distance (v) between the lens and the imaging position. The equation shows that the reciprocal value of the focal length (f) equals the reciprocal value of the object distance added to the reciprocal value of the image distance. In general, the object distance is a large value as compared to the image distance. The image distance approaches the focal length according to the imaging equation.
The camera with correct focusing condition can acquire a clear image. The clear image can be obtained when the camera has a proper image distance. However, the focal length for the lens may be improperly changed due to external factors. For example, the change of temperature may vary the lens due to effect of thermal expansion. Further, the change of temperature may vary the refractive index of the lens. The variations in the lens therefore may make changes in the focal length of the camera, and cause error imaging. To solve the error, a temperature compensation mechanism is applied in the conventional technology. The temperature compensation mechanism is employed to compensate the change of the focal length due to the effect of temperature. Therefore the relationship between the focal length and the image distance may lead to calibrating image distance and allow clear imaging onto the image sensor through the lens.
The temperature compensation mechanism may be implemented by incorporating an object in which its shape can be changed with the change of temperature. When the camera is disposed with this mechanical design utilizing the object, the change of focal length of the assembly of lens and image sensor due to the temperature variation can be well compensated for.
The mentioned object is characterized in that its shape can be changed with the change of temperature. For example, the temperature rise may change the outer curve of the object; and the curve is in opposite direction when the temperature drops. Through this mechanism, the distance between the lens and the image sensor can be calibrated.
In an example, the object implementing the temperature compensation mechanism may be made of composite materials which are assemblies of at least two materials. The two materials have different characteristics reacting to the effect of thermal expansion with change of temperature. When the curve of composite materials is in a specific direction due to the change of temperature, the variation of focal length is compensated for.
According to the temperature compensation mechanism applied to the conventional lens module, one of the solutions is to introduce a compensation flake disposed between the lens and the lens holder. The bendable compensation flake may bring the lens to move along the direction of optical axis. The movement keeps the imaging plane of the lens module over a preset plane surface.